1. Field of the Invention
This invention relates generally to incinerators, and more particularly, but not by way of limitation, to an improved, self-supporting incinerator having a combustion chamber and a stack.
In one aspect, the present invention relates to an improved shield assembly for use in combination with a stack wherein the shield assembly is adapted to expand independently of the expansion of the stack.
2. Brief Description of the Prior Art
In certain refinery operations hydrogen sulfide and other sulfur bearing compounds are removed from sour gas refinery streams in order to provide sweet gas streams. Further, other refinery operations produce hydrogen sulfide and other sulfur bearing compounds which must be processed through sulfur recovery systems; even so, the effluent or tail gas from such sulfur recovery systems contain residual sulfide products. The sulfide so removed or produced must be disposed of in an economical manner. Thus, the hydrogen sulfide is often burned in a gas incinerator and the combustion products vented to the atmosphere via a stack.
The recovery or removal of sulfur bearing compounds such as hydrogen sulfide from refinery operations often results in the formation of a plume external to the stack of the incinerator or sulfur recovery system through which the effluent or tail gases from such refinery operations are vented to the atmosphere. The plume formation is an aerosol effect resulting from the reaction of the sulfur containing effluent or tail gas and moisture in the atmosphere as the effluent or tail gas cool after leaving the stack of the incinerator or sulfur recovery system. The plume, is highly corrosive, may be irritating to a person's eyes, nose and throat, may cause crop damage, and is generally a violation of certain governmental regulations.
Incinerators for the burning of a tail gas, such as hydrogen sulfide, or the burning of other sulfur bearing effluents, have heretofore been known. Generally the prior art devices include a refractory lined combustion chamber and a tall stack. The combustion in such prior art devices generally occurs in the housing portion of the assembly and is vented to the atmosphere through the stack. Of prime concern in the use of such incinerators is the adequate dispersal of sulfur dioxide into the atmosphere to prevent the formation of an undesirable ground concentration of pollutants. The main factors which affect the ground concentration of the pollutants are the rate of release of the pollutant from the stack, the temperature of the stack gases, and atmospheric conditions. In many instances one must employ a very tall stack to ensure adequate dispersal of sulfur dioxide into the atmosphere.
However, problems have been encountered in the prior art devices when burning hydrogen sulfide in that if the combustion products remain in the incinerator and stack for a period of time greater than about 20 seconds the sulfur dioxide produced by the burning of the hydrogen sulfide reacts with oxygen to form sulfur trioxide which can subsequently react with water, either in the apparatus or the atmosphere, to produce sulfuric acid. Sulfuric acid fumes, when vented from the stack, combine with water vapor and are cooled. When the dewpoint temperature is reached, a dense opaque plume consisting of sulfuric acid aerosol mist is formed. This resulting plume is highly corrosive to practically everything which it contacts.
In addition, many of the prior art incinerators are provided with an outer shell surrounding the stack, the outer shell serving as a rain and heat shield to prevent corrosion of the stack, as well as controlling deflection due to temperature differences. However, problems have been encountered in the prior art devices in that the prior art shields are not capable of expanding when the stack of the incinerator is thermally expanded. Thus, the shields are often damaged as the result of the thermal expansion of the stack, or the stack itself is damaged due to resistance to thermal expansion of the stack by the outer shell serving as the rain or heat shield. Also, the shields of the prior art devices have been very expensive to install because the shields are easily damaged during erection of the stack if the shields are connected to the stack at ground level. Thus, to prevent damage to the shields the shields have been connected to the erected stack which may extend several hundred feet above the ground, and complex banding and clip assemblies have been devised for the shield installation, making it difficult to install the shield at elevated heights.
Thus, a need has long existed for an improved incinerator wherein the residence time of the combustible materials in the incinerator can be more effectively controlled to insure that when burning certain gases in the incinerator, such as hydrogen sulfide, the residence time of the gas in the incinerator and stack is sufficiently short to prevent the conversion of the sulfur dioxide into the undesired sulfur trioxide component which can thereafter react with the water in the apparatus or the atmosphere to produce a heavy grey sulfuric acid plume. It is also highly desirable that the apparatus be equipped with a rain and heat shield which will not be damaged, or cause damage to the stack of the incinerator, when the stack is expanded as a result of the heat gradient placed on it as a result of the combustion of the gases in the incinerator. Further, it would be most advantageous if the rain and heat shields could be connected to the stack with simple tools.